Operational constraints

It's our job to ensure we have enough secure power in real time. At times, we may have to dispatch or call in some power generators differently from the wholesale power market schedule. This prevents overloads and maintains enough generation reserve. It may also happen because of generator testing.

When power stations run differently to the market schedule, it's called a constraint. Constraint payments account for the difference between the market schedule and what actually happened. They keep generators financially neutral. This is subject to firm access and the Trading and Settlement Code.

Generators can be constrained:

There is always an overall net cost to the system associated with constraints. More details on constraint payments are in the Balancing Market Principles Statement.

Sometimes network limitations mean we need to change the output to the grid for particular generators. In this case, the generator may be eligible for financial compensation. This is known as firm access. The basis is set out in the Trading & Settlement Code.

In advance of firm access being available, some generators may opt to connect to the system on a “non firm” basis. In this instance, the generator will not receive financial compensation if we must change their output. 

Firm access is linked to associated transmission reinforcements (ATRs).

ATRs are new or upgraded transmission infrastructure projects. The ATR must be complete to release the generator’s firm access allocation. To achieve firm access in the single electricity market, the project must also already be connected via its permanent connection.

We publish ATR status updates quarterly. They show progress for projects against their estimated completion date. Changes to scheduled FAQ dates will be notified in writing.